The invention relates to a method for producing an adhesive screw connection between at least one upper component and at least one lower component using a flow drill screw.
The invention also relates to a flow drill screw usable therefor.
Producing an adhesive screw connection between components by adhesive bonding and flow drill screwing is sufficiently well known from the prior art. In this respect, reference is made for example to German patent document no. DE 103 48 427 A1. The operation of chipless flow drill screwing and thread forming and also a suitable hole- and thread-forming or flow-drilling screw are graphically represented in German patent document no. DE 39 09 725 C1.
In particular when the upper component has a material thickness and/or hardness that is unsuitable for flow drill screwing or is formed from a material that is unsuitable for flow drill screwing (for example FRP), the upper component may have a predrilled hole, as shown in German patent document no. DE 10 2012 210 791 A1. During the screwing-in operation, the screw tip and then the self-forming thread portion of the flow drill screw meets the previously applied layer of adhesive, whereby the adhesive is swirled up and thrown out of the predrilled hole. This leads to contamination of the screwing-in device and/or the components. Furthermore, the adhesive escaping from the predrilled hole may impair the torque control of the screwing-in device. Until now, the joining or screwing-in location has therefore been omitted from an application of adhesive. However, the adhesive-free portion makes the application of adhesive more complicated and leads to an interrupted adhesive seam or adhesive area.
The invention is based on the object of providing a method for producing an adhesive screw connection between at least one predrilled upper component and at least one lower component using a flow drill screw that does not have at least one disadvantage that the prior art entails, or only at least to a reduced extent.
This object is achieved by the method according to the invention for producing an adhesive screw connection between at least one predrilled upper component and at least one lower component using a flow drill screw, wherein the screw penetrates the upper component at the joining location through a predrilled hole and is screwed to the lower component to form a flow-drilled hole, and there is provided at least one protective ring or a protective sleeve, through which the screw shank is screwed during the screwing-in operation in the predrilled hole of the upper component.
The method according to the invention is preferably performed in an automated manner. A number of upper, predrilled components and/or a number of lower components may be provided. The components are adhesively bonded to one another at their mutually facing surfaces. The adhesive may be applied over the surface area or along at least one path (for producing an adhesive seam).
A flow drill screw, i.e. a screw that is suitable for chipless flow drill screwing and thread forming, has a screw shank with a hole-forming portion, extending from the tip of the shank or screw, and a self-forming thread portion, adjoining in the direction of the screw head.
The protective ring has a shorter axial length than the screw shank and can move in the axial direction in relation to the screw shank (i.e. an axial mobility is provided between the protective ring and the screw shank of the flow drill screw). The protective ring preferably is formed with a smaller outside diameter in comparison with the diameter of the predrilled hole in the upper component, so that it can be introduced or inserted into the predrilled hole without pressing. After the screwing-in operation, the protective ring remains in the predrilled hole.
During the screwing in, the protective ring is supported within the predrilled hole in the upper component against the lower component, whereby the axial relative movement between the screw shank and the protective ring is made possible in such a way that the fixed protective ring and the screw head of the screwing-in screw approach one another during the screwing-in operation. The screwing-in operation has two phases (flow drill screwing and thread forming with simultaneous thread engagement).
The protective ring serves on the one hand for preventing adhesive from escaping during the screwing-in operation. In particular, the adhesive is prevented from being drawn up by the self-forming thread of the screw. The components and the screwing-in device (including the clamping tools used) are consequently not contaminated by escaping adhesive. The application of adhesive may take place continuously or over the full surface area, whereby the application, in particular automated application, is facilitated and advantages are also obtained with regard to the achieved strength of the connection and the corrosion behavior at the joining location. Furthermore, the torque control, if provided, remains stable. On the other hand, however, the protective ring may also serve for the centering and guiding of the screw shank within the predrilled hole during the screwing-in operation and prevent contact between the rotating screw shank and the inner wall of the predrilled hole (that is to say so-called seizing between the screw shank and the wall of the predrilled hole is prevented). Furthermore, improved corrosion resistance can be achieved by the protective ring remaining in the predrilled hole. In particular, contact corrosion (for example due to exposed CRP fibers of the upper component) can be avoided. This is not an exhaustive list of advantages that accompany the invention.
The protective ring may be fastened to the screw shank and inserted together with it into the predrilled hole in the upper component. This leads to a simplification of the method sequence and to better automatability.
Preferably, the axial length of the protective ring corresponds at most to the thickness of the upper component. In other words, the axial length of the protective ring does not exceed the thickness of the upper component. As a result, the protective ring has sufficient space in the predrilled hole in the axial direction, whereby the screwing-in operation is also not impaired.
Similarly, it may be provided that the protective ring is deformable and formed with an excess length in the axial direction in comparison with the thickness of the upper component, whereby it is compressed between the lower component and the screw head during the screwing-in operation. When being compressed, the protective ring is deformed, in particular plastically, for which purpose it is formed from a deformable material, such as for example plastic (including plastic composite materials) or metal (for example a soft aluminum material). The wall of the ring may have structural weakening features, which make selective and/or facilitated compression possible, and with it improved flowing of the material of the ring. Such weakening features may be for example impressions or slits in the wall of the ring. The compression allows bearing pressure of the projected area within the predrilled hole in the upper component to be brought about, with the effect of preventing slipping of the components at the joining location, in particular until the curing of the adhesive. Furthermore, the compressing of the ring allows the sealing off of the predrilled hole to be improved, thereby also reliably preventing outgassing, for example in the cathodic electrophoretic painting process (with the risk of blistering).
It may similarly be provided that the protective ring is stiff and formed with an excess length in the axial direction in comparison with the thickness of the upper component, whereby a defined gap occurs or is produced between the components during the screwing-in operation. This defined gap serves for example as an adhesive gap. As a result, displacement of adhesive and/or direct contact of the components at the joining or screwing location can be prevented. The stiff protective ring is for example formed from metal, in particular from a steel material or hard aluminum material.
On account of the pressing achieved at the joining or screwing-in location, during the screwing in of the flow drill screw the adhesive can penetrate into the predrilled hole, as it were from below, and fill cavities and/or adhesively bond the protective ring within the predrilled hole. As a result, on the one hand the sealing off is improved and on the other hand the achievable strength of the connection is increased. The adhesive applied continuously or over the full surface area for the adhesive bonding of the components may therefore also serve within the scope of the invention for achieving a functional use within the predrilled hole. As already explained at the beginning, by contrast it is provided in the prior art that the joining or screwing-in location is omitted from an application of adhesive. It is provided with preference that, during the application of the adhesive, more adhesive is applied altogether or only locally at the screwing-in or joining location, and then, during the screwing in of the flow drill screw, the adhesive can penetrate into the predrilled hole from below.
A flow drill screw according to the invention has a screw head and a screw shank formed on the latter, with a hole-forming portion extending from the tip of the shank and a self-forming thread portion adjoining in the direction of the screw head. A captively held protective ring is arranged on the screw shank. The flow drill screw and the protective ring are accordingly formed in a one-part manner, i.e. as one part.
The protective ring preferably is arranged in the transitional region between the hole-forming portion and the self-forming thread portion on the screw shank and is securely held on the screw shank, in particular by clamping or by a clamping fit and/or by a form fit (for example with the thread turns of the thread portion). Depending on the strength of the clamping fit and/or the form fit, the screw shank may slide through the protective ring in the axial direction or be screwed through the protective ring by the self-forming thread portion. In both cases, an axial relative movement between the flow drill screw or its screw shank and the protective ring, which in the process is supported on the lower component, is obtained during the screwing-in operation.
The protective ring may be formed from metal (for example aluminum) or from plastic (for example PA 4.6). The protective ring may be fitted or screwed onto the screw shank. Furthermore, a releasable fixing, for example by spot adhesive bonding, is also possible. In particular if it is formed from plastic, the protective ring may also be molded onto the screw shank.
With preference, the protective ring fastened or held on the screw shank at least partially covers over the hole-forming portion and in particular also the screw tip. As a result, the protective ring, formed in particular in the manner of a sleeve, may also act as a guard during transport and storage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.